The invention relates to a controller for controlling an actuator for a magnetic valve, and more specifically to a controller for an electromagnetic actuator for driving a valve of an engine mounted on such apparatus as an automobile and a boat.
Valve driving mechanism having an electromagnetic actuator has been known and called a magnetic valve. An electromagnetic actuator typically includes a moving iron or an armature, which is placed between a pair of springs with given off-set load so that the armature positions at an intermediate part of a pair of electromagnets. A valve is connected to the armature. When electric power is supplied to the pair of electromagnets alternately, the armature is driven reciprocally in two opposite directions thereby driving the valve. Conventionally, the driving manner is as follows.
1) The magnetic attraction power that one of the electromagnets provides to the armature overcomes rebound power by the pair of springs and attracts the armature to make it seat on a seating position. The armature (valve) is released from the seating position by such a trigger as suspension of power supply to the electromagnet, and starts to displace in a cosine function manner by the force of the pair of springs.
2) At a timing according to the displacement of the armature, an appropriate current is supplied to the other electromagnet to produce magnetic flux that generates attraction force.
3) The magnetic flux rapidly grows as the armature approaches the other electromagnet that is producing the magnetic flux. The work by the attraction power generated by the other electromagnet overcomes the sum of (i) a small work by the residual magnetic flux produced by the one electromagnet which acts on the armature to pull it back and (ii) a mechanical loss which accounts for a large portion of the sum of work. Thus, the armature is attracted and seats on the other electromagnet.
4) At an appropriate timing as the armature seats, a constant current is supplied to the other electromagnet to hold the armature in the seated state.
Thus, as an armature nears a seated state side, magnetic attraction power becomes big rapidly. In addition, excessive electric power may be supplied in order to realize stable seating. Seating speed may become larger than 1 m/s, for example, generating undesired sound when seating is done. Various techniques have been proposed for lowering the seating speed.
For example, Japanese Patent Application Unexamined Publication (Kokai) No. 10-274016 describes a scheme wherein when making an armature (movable element) seat, power is supplied to an electromagnet for a first predetermined period, followed by suspension of power supply for a second predetermined period, and then power supply to the electromagnet is resumed. When power supply is suspended, attraction power to attract the armature lowers rapidly. However, the armature continues to move by inertia. When power supply is resumed, the attraction power increases again. The first predetermined period and the second predetermined period are determined according to the position of the armature. Thus, seating speed of the armature is finely adjusted to reach a seated state.
Conventionally, to supply electric power to perform over-excitation for an electromagnet of the electromagnetic actuator, there are such schemes as to supply constant current and to apply constant voltage. In such power supply schemes, magnetic attraction power increases sharply resulting in collision of the armature to a seating surface.
As a specific example, assume that electromagnetic actuators are used to drive a valve train of an engine at high speed, that constant voltage is applied during over-excitation period, and that optimization is performed to lower the seating speed of the armatures. Referring to FIG. 18, the left vertical scale shows displacement (mm) and speed (m/s) of an armature as well as current (A) supplied to the electromagnet. The right vertical axis shows attraction power (N), and voltage applied to the electromagnet (V).
At time t1 (time zero), power supply to the electromagnet is suspended, and the armature that has been seated in a closed valve state is released. In response to this, displacement of an armature begins to increase. Here, the displacement has been xe2x88x920.2 mm, which is a clearance between a closed position of the valve shaft and the armature when the valve is closed. The clearance enables the valve to completely close an exhaust/intake opening. At about time t2 (0.8 ms), armature speed sharply drops. This means that the clearance reaches 0 mm as the armature is released and collide and Join with the static valve shaft. The armature is now capable of driving the valve shaft.
At about time 3.2 ms, over-excitation voltage is applied to the electromagnet. As the armature approaches an open valve position, magnetic attraction power rapidly increases. Immediately after the armature is seated in an open valve position, the attraction power exceeds a minimum holding force (400N), which is minimum force for maintaining a seated state. Thus, the armature is held in the seated state. Over-excitation finishes around time t3 (4.2 ms). Then, a constant current control for holding the armature in the seated position starts. As shown in the drawing, seating speed at time t3 is about 0.5 m/s, which is not small enough. However the starting and finishing time of over-excitation is adjusted, it is difficult to control the seating speed to a substantially small value.
The scheme described in the above mentioned Kokai No. 10-274016 is not capable of prevention collision of the armature to a seating. Thus, there is a need for a controller for an actuator which provides a low seating speed of the armature, thereby preventing the armature from generating large noise when it reaches and seats on a seating surface.
According to one aspect of the invention, a controller for an electromagnetic actuator comprises a pair of spring acting in opposite directions, and an armature coupled to a mechanical element. The armature is connected to the springs and held in a neutral position given by the springs when the actuator is not activated. The actuator includes a pair of electromagnets for driving the armature between two end positions. The controller includes voltage application means for applying voltage to an electromagnet corresponding to one end position for a first predetermined period so as to attract the armature to the end position. The controller also includes a peak current detector for detecting the peak of current flowing through the electromagnet in the first predetermined period. In accordance with the peak value, a decision means decides the application period of voltage that is to be applied to the electromagnet after the first application period has elapsed.
According to one aspect of the invention, because the voltage application period is determined according to the peak current, the armature can seat with a controlled seating speed without generating substantial noise.
According to one embodiment of the invention, the decision means for deciding the voltage application period decides the voltage to be applied to the electromagnet after the first application period in accordance with the peak current detected by the peak current detector. In this manner, the armature can seat with a seating speed which does not do generate undesired noise.
According to another aspect of the invention, the decision means for deciding the voltage application period decides a second application period for a second voltage and a third application period for a third voltage in accordance with the peak current detected by the peak current detector. The voltage application means applies the second voltage to the electromagnet over the second determined application period after the first application period has elapsed. Then, the voltage application means applies the third voltage to the electromagnet over the third application period. The second voltage is lower than the first voltage, and the third voltage is set higher than the second voltage. In this manner, attraction power is controlled such that the armature seats with a lower seating speed.
According to another aspect of the invention, the controller further comprises magnetic flux estimation means for estimating magnetic flux that the electromagnet attracting the armature generates when driving the armature from one end position to the other end position. The controller further comprises means for controlling power supply to the electromagnet such that magnetic flux estimated by the magnetic flux estimation means converges into the magnetic flux that is required for holding the armature in the other end position after voltage application to the electromagnet for the period decided by the voltage application period decision means finishes.
In this manner, magnetic flux generated from the electromagnet is controlled to converge into the magnetic flux that is necessary for holding the armature. Thus, a stable attraction force is produced enabling stable seated state of the armature.
According to yet another embodiment of the invention, the controller further comprises magnetic flux estimation means for estimating magnetic flux that the electromagnet attracting the armature generates when driving the armature from one end position to the other end position. The controller further includes means for controlling power supply to the electromagnet after the first application period elapsed, such that magnetic flux estimated by the magnetic flux estimation means converges into magnetic flux that is predetermined based on the peak current detected by the peak current detector.
In this manner, because magnetic flux generated from the electromagnet is controlled to converge into magnetic flux that is predetermined based on the peak current, a stable attraction power at the time of seating and after seating is produced, enabling seating without generating substantial noise and enabling maintenance of stable seating state.